The existence of rotational imbalance in spinning components is typically an undesirable situation. The prior art is replete with various methods and devices for determining and/or correcting such imbalance. These devices are generally divisible into two categories, those for determining static imbalance and those for determining dynamic imbalance.
Static imbalance in any solid article is the result of an asymmetric mass distribution within the article, and may be determined by simply balancing the article at its center point. Dynamic imbalance, on the other hand, may occur in an object having a symmetrical mass distribution, occurring when the primary inertial axis of the rotating object is not colinear with the axis of rotation. The effects of a dynamic imbalance in a statically balanced component are thus detectable only during rotation.
The use of ball bearings to support rotating shafts or other moving components is well known throughout the modern industrial world. In a typical ball bearing arrangement for a rotating shaft, a plurality of spherical bearing balls are disposed between concentric inner and outer bearing races for providing rolling contact between the bearing support and the rotating shaft. For high speed, high load applications, dimensional uniformity of the individual bearing balls is a necessity, requiring careful manufacture and close inspection. Such measures have resulted in individual bearing balls with consistently uniform weight, diameter, surface finish, etc.
Despite the close tolerances being met by today's manufacturers, individual balls still continue to wear and degrade unevenly under certain high demand applications. It has been theorized that such wear is the result of the existence of dynamic imbalance in individual bearing balls. A dynamically unbalanced ball tends to roll about an axis coincident with the ball's principal moment of inertia, thus causing a particular circumferential portion of the individual ball to receive the bulk of the contact between the ball and associated races. A dynamically balanced ball would tend to rotate randomly, distributing contact over its entire surface.
Prior art dynamic test machines have typically been directed toward balancing elongated roller bearings, shafts, and other non-spherical rotating components. What is needed is a device for evaluating the degree of dynamic imbalance in a geometrically symmetrical spherical body.